Periodic precipitation of silver chromate/dichromate in gelatin

Lexa, Dusan; Holba, Vladislav

doi:10.1007/bf00652771

Cited by 8 publications

(13 citation statements)

References 10 publications

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“…For later measurements with similar results on the formation of a region of colloid (turbidity front) prior to the appearance of a band in the silver chromate/dichromate system, see ref 41 and Table 1, line 11.…”

Section: Analysis Of Some Selected Experimentsmentioning

confidence: 76%

Spatial Structure Formation in Precipitation Reactions

Müller

Ross

2003

J. Phys. Chem. A

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We analyze selected experiments on spatial structure formation in the presence and the absence of imposed gradients of concentrations, with emphasis on length scales, time scales, initial degree of supersaturation, and initial concentration differences of the ions forming the precipitate. In relation to these experiments, we discuss two major proposed models. The first is the Ostwald-Prager model of Liesegang bands for systems with imposed concentration gradients (diffusion of ions occurs and at a given degree of supersaturation, nucleation and precipitation to form bands take place discontinuously but repeatedly in space) The other model, known by various designations (Ostwald ripening, competitive growth model, Turing instability) for systems with and without imposed gradients, supposes nucleation to occur continuously in a region of space, followed by the competitive and autocatalytic growth of larger particles at the expense of the dissolution of smaller particles within that region of space. This process coupled to diffusion may lead to macroscopic Turing structures. We find extensive experimental evidence for the second model over a large range of initial concentrations of electrolytes as well as some theoretical evidence, and we find the experimental evidence presented for the validity of the first model alone to be insufficient.

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Section: Analysis Of Some Selected Experimentsmentioning

confidence: 76%

Spatial Structure Formation in Precipitation Reactions

Müller

Ross

2003

J. Phys. Chem. A

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“…As the diffusion front proceeds, the precipitate is deposited in the form of bands at specific distances. 5,6 A large number of Liesegang systems consisting of hydroxides, 7,8 sulfides, 9 chromates and dichromates, 10 and phosphates 11,12 are reported.…”

Section: Introductionmentioning

confidence: 99%

Revert Banding in One-Dimensional Periodic Precipitation of the (AgNO₃ + KBr) System in Agar Gel

et al. 2019

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A periodically precipitating system wherein interband distance successively decreases is known as revert Liesegang banding. The phenomenon is rare, and the underlying mechanism is implicit. In the present paper, the Liesegang system comprising of AgNO 3 and KBr as the outer and inner electrolyte pair showing revert banding in agar gel by employing a 1D experimental setup is studied under varying concentrations of participating species. Revert banding was observed under all the experimental conditions. The concentrations of inner and outer electrolytes were found to play a major role in reverting since they build the ionic strength inside Liesegang tubes. We hypothesize that the band reverting is the interplay of van der Waals and electrical double-layer interactions, and hence classical DLVO (Derjaguin–Landau–Verwey–Overbeek) theory can be applied to interpret reverting. We propose that revert deposition of precipitates is the outcome of flocculation and peptization of sols, which is the manifestation of balancing attractive and repulsive interactions acting on colloidal particles responsible for band formation.

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“…Diffusion of a drop of silver nitrate solution, AgNO 3 , through a gel matrix containing potassium dichromate, K 2 Cr 2 O 7 , will lead to the periodic precipitation of silver dichromate, Ag 2 Cr 2 O 7 (Grzybowski, 2009;Liesegang, 1896). The initial explanation for this phenomenon was based on identifying two characteristics that the involved substances needed to satisfy: one of them is that the salt obtained as reaction product must have little solubility, that is to say, it must have a rather small ionic dissociation constant or solubility product constant (2.7x10 -11 for silver dichromate, (Lexa & Holba, 1993), and the other one is that the salts' diffusion rates were different, 1.5x10 -9 m 2 /s for dichromate (Rod & Vacek, 1986) and 1.5x10…”

Section: Spatio-temporal Structures and Reaction-diffusion Systems: Fmentioning

confidence: 99%

Patrones en la naturaleza: más que un diseño inspirador

Serna

2017

Rev. Acad. Colomb. Cienc. Ex. Fis. Nat.

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At all scales and both in animate and inanimate systems, nature displays a wide variety of colors, rhythms, and forms. For decades, these natural patterns and rhythms have been studied and used as a source of inspiration for the technological development and well-being of human beings. Today we understand that the design of these patterns responds to principles of functionality and efficiency. This article focuses on physicochemical aspects to show how the study of spatiotemporal patterns became such an important area of interest and research for natural sciences. In particular, we address some systems in which the formation of patterns is explained by the coupling between chemical and transport processes, such as chemical gardens, periodic precipitation and Turing patterns. © 2017. Acad. Colomb. Cienc. Ex. Fis. Nat. Key words: Turing patterns; Morphogenesis; Periodic precipitation; Energy Economy; Bio-inspired processes. Patrones en la naturaleza: más que un diseño inspirador ResumenEn la naturaleza observamos una amplia variedad de colores, ritmos y formas, a toda escala y en sistemas animados e inanimados. Desde hace décadas los patrones y ritmos de la naturaleza han sido objeto de estudio y fuente de inspiración en el desarrollo tecnológico y en el bienestar del ser humano. Hoy entendemos que el diseño de los patrones de la naturaleza obedece a principios de funcionalidad y de eficiencia. En este artículo nos enfocamos en aspectos fisicoquímicos para mostrar cómo el estudio de los patrones espacio-temporales se convirtió en un área de gran interés e investigación en ciencias naturales. En particular, abordamos algunos sistemas donde la formación de patrones se explica mediante el acople entre procesos químicos y de transporte, tales como los jardines químicos, la precipitación periódica y los patrones de Turing.

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Periodic precipitation of silver chromate/dichromate in gelatin

Cited by 8 publications

References 10 publications

Spatial Structure Formation in Precipitation Reactions

Spatial Structure Formation in Precipitation Reactions

Revert Banding in One-Dimensional Periodic Precipitation of the (AgNO₃ + KBr) System in Agar Gel

Patrones en la naturaleza: más que un diseño inspirador

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Periodic precipitation of silver chromate/dichromate in gelatin

Cited by 8 publications

References 10 publications

Spatial Structure Formation in Precipitation Reactions

Spatial Structure Formation in Precipitation Reactions

Revert Banding in One-Dimensional Periodic Precipitation of the (AgNO3 + KBr) System in Agar Gel

Patrones en la naturaleza: más que un diseño inspirador

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Product

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Revert Banding in One-Dimensional Periodic Precipitation of the (AgNO₃ + KBr) System in Agar Gel